Pressure sensors measure the compression and stretching (tension) of materials, and have many industrial, commercial and medical applications. Pressure sensors based on piezoresistive effects have been constructed using several different types of materials and films including metal films (with a gauge factor lower than 4) and silicon (with a gauge factor ranging from 60 to 200). Silicon based pressure sensors are normally manufactured using micro-electromechanical system (MEMS) technology, and have been extensively used in many fields including disposable sensors for medical applications, process control, and the automobile industry.
While silicon-based technology has been a driving factor in developing cost effective pressure sensors, recent advances in technologies other than silicon demonstrate that there are favorable alternatives to silicon in some applications. For example, MEMS technology in plastic materials has shown measurable promise as an alternative to silicon MEMS.
Additionally, homogeneous thin polymer films have recently been prepared by organic synthesis and have been proven to possess piezoresistive (PZR) effect. These films have a gauge factor in the range of 8 to 31 depending on the processing method. There are two classes of PZR thin polymer films commonly used. In a first class, the PZR effect is obtained in a thin film by nitrogen implantation in polymers like polyimides, polyacrylonitriles, polysulfones, and polyesters. In a second class, the PZR effect is obtained directly by spin coating a solution composed of poly anisidine p-toluene sulfonate dissolved in N,N-dimethylformamide. From these PZR thin polymers, a PZR film based on polyaniline is obtained, whose gauge factor is around 8, and whose electrical resistivity may be as low as 10.6 ohm*cm for a layer thickness of 3.8 micrometers.
In addition to spin coating, a thin film can be obtained from a liquid phase by means of dip coating and spray coating, in which a sol-gel transition occurs at the end of each casting process. However, spin coating, dip coating, and spray coating all suffer from the fact that the resulting film is deposited on the whole surface of a substrate, and subsequent photolithographic and etching processes are needed to obtain a patterned film. Consequently, a large quantity of film is wasted during both the coating and removal processes.